In standard cardiopulmonary resuscitation (CPR), rescuers switch between ventilation and chest compressions. We examined the effect of this task-switching requirement on chest-compression quality to gain insights into the cognitive mechanisms underlying performance in standard CPR. Understanding these mechanisms can help in the development of evidence-based practical implications and cognitive aids for CPR.A total of 300 first-year medical and dentistry students (212 females, 20.2 ± 4.4 years) participated in this randomized controlled trial. They received either a CPR training comprising both chest compressions and ventilation (standard CPR) or a CPR training comprising chest compressions only (chest-compression-only CPR). Chest-compression quality (compression depth and rate) was measured via a resuscitation manikin and analyzed using linear mixed models and linear trend analyses.Overall, chest-compression quality did not differ across standard CPR and chest-compression-only CPR. However, in standard CPR, compression quality was better after ventilation than before ventilation. Importantly, ventilation impaired the quality of the compressions executed immediately after ventilation, but the quality increased with each compression after ventilation, resulting in a better chest-compression quality after ventilation than before it.This study suggests that ventilation acts as a break, improving physical capability, which in turn enhances compressions after ventilation. However, at the same time, ventilation causes a task switch which increases cognitive demands and impairs chest-compression quality immediately after ventilation. Considering the negative effect of the task-switching demand on chest-compression quality, it is useful to develop cognitive aids for professional medical care. Such cognitive aids can signal an upcoming switch to ventilation, thereby reducing the multitasking load in terms of reduced monitoring demands with respect to the number of chest compressions that have already been executed.